There are not only callbacks, but also event emitters. In you client
"conn.on('data', .." listens to an event emitter, it could be called
multiple times, as long the connection exists. Node exists when you
are no longer waiting for any event, neither event emitter or
callback.On Thu, Mar 15, 2012 at 6:53 AM, C. Mundi <[email protected]> wrote: > I know *what* the following code does. I want to understand *why*. > > Consider the following client/server pair: > > client.js > var net = require('net'); > var conn = net.createConnection(8000, function() { // 'connect' listener > console.error('connected to server'); > conn.on('data', function(data) { > var msg = data.toString(); > console.error('Got data: ' + msg); > conn.write('Back at ya!'); > conn.end(); // Pay close attention! > }); > }); > > server.js > var net = require('net'); > var server = net.createServer(function(client) { > console.error('Accepted connection'); > client.on('end', function() { > console.error('Client has closed connection.'); > }); > client.on('data', function(data) { > var msg = data.toString(); > console.error('Got data: ' + msg); > }); > client.write('Welcome'); > }); > > server.listen(8000, function() { > console.error('Listening on port 8000'); > }); > > So we start the server ('node server.js') and then we run the client ('node > client.js') and see (as expected) that the server accepts the connection > from the client, they exchange a pair of messages and the client exits. Now > let's comment out the 'conn.end()' from the client. Now the client hangs > around until we kill it. What I want to understand is this: how does the V8 > thread know that it should or should not hang around? The conn.end() is in > the 'connect' event listener, which gets registered only after the > connection is established. (And it is important to notice that if the > connection had been refused, then the client would have exited with an > error.) My mental model goes like this, and I would like some feedback: > > During the execution of each event loop, node memoizes every async call long > enough to see if the callback could be called. As long as there is at least > one pending callback (and no error or explicit exit() call) the event loop > keeps running. Ok. Now let's suppose the server accepts the connection. > The 'connect' event is caught by the listener callback in the client. And > after this 'connect' callback executes... node hangs around, because the > 'connect' callback registered a callback for the 'data' event. And event > handlers are persistent, so execution keeps looping if the conn.end() is not > present. Now, somehow, conn.end() breaks us out of the loop, at which point > there is nothing left to do *and* nothing left to wait for, so client.js > exits. My guess is that the conn.end() call unregisters all the event > handlers associated with the connection object conn, at which point node has > nothing left to do. > > Am I even close to the right way of thinking about this? > > Thanks! > > -- > Job Board: http://jobs.nodejs.org/ > Posting guidelines: > https://github.com/joyent/node/wiki/Mailing-List-Posting-Guidelines > You received this message because you are subscribed to the Google > Groups "nodejs" group. > To post to this group, send email to [email protected] > To unsubscribe from this group, send email to > [email protected] > For more options, visit this group at > http://groups.google.com/group/nodejs?hl=en?hl=en -- Job Board: http://jobs.nodejs.org/ Posting guidelines: https://github.com/joyent/node/wiki/Mailing-List-Posting-Guidelines You received this message because you are subscribed to the Google Groups "nodejs" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/nodejs?hl=en?hl=en
